1. Field of the Invention
The present invention relates to a control device of an internal combustion engine, that controls an operation state of the internal combustion engine in which a lubricant circulates through each sliding portion.
2. Description of the Background Art
An exhaust gas exhausted when an internal combustion engine (hereinafter, also referred to as an engine) such as a gasoline engine or a diesel engine is driven contains substances of whose emission into the atmosphere is not preferable. In particular, the exhaust gas from the diesel engine contains particulate matter (PM) mainly composed of carbon, soot, soluble organic fraction (SOF), and the like, all of which cause air pollution.
As an apparatus for purifying the particulate matter (hereinafter, referred to as PM) contained in the exhaust gas, an exhaust purifying apparatus, in which a particulate filter is arranged in an exhaust manifold of the diesel engine so as to collect PM contained in the exhaust gas passing through the exhaust manifold, thus reducing an amount of emission into the atmosphere, has been known. For example, a diesel particulate filter (DPF) or a diesel particulate-NOx reduction system (DPNR) catalyst is used as the particulate filter.
When the particulate filter is used to collect the PM and if an amount of deposit of the collected PM increases, the particulate filter is clogged. If clogging of the filter takes place, increase in pressure loss of the exhaust passing through the particulate filter as well as corresponding increase in exhaust back pressure of the engine take place, which results in lower engine output and lower fuel efficiency.
In order to solve such a problem, conventionally, a temperature of the exhaust is raised at a time point when the amount of PM collected by (deposited on) the particulate filter reaches a certain level, so that the PM on the particulate filter is burnt and removed to recondition the particulate filter.
As a reconditioning method, for example, a small amount of fuel is auxiliarily injected (post-injection) after main fuel injection and before closing of an exhaust valve, in order to raise the temperature of the exhaust gas and to burn the PM deposited on the particulate filter (see, for example, Japanese Patent Laying-Open No. 2004-211638). It is noted that post-injection may be performed not only for filter reconditioning treatment but also for improvement in engine performance.
Here, it has been known that, as a result of post-injection, a part of injected fuel adheres to a wall surface in a cylinder, the adhered fuel dilutes the engine lubricant, and viscosity of the engine lubricant is lowered. It has also been known that, when viscosity lowers with higher temperature of the engine lubricant, lubrication of each sliding portion of the engine tends to be insufficient (see, for example, Japanese Patent Laying-Open No. 8-177432).
In the diesel engine, a maximum combustion pressure has increased as a result of technological progress in a commonrail, an injector (a fuel injection valve), and the like. In addition, recently, in order to improve fuel efficiency of the engine, an engine lubricant of low viscosity is used to reduce friction. Moreover, for further lower friction, a width of a sliding portion such as a bearing has been made smaller.
Such increase in the maximum combustion pressure, lower viscosity of the lubricant, and smaller width of the bearing are effective for improvement in engine performance and fuel efficiency. On the other hand, load imposed on the bearing (load due to combustion pressure) is increased, which means an environment disadvantageous in terms of seizure of the bearing.
If the lubricant is diluted as a result of post-injection or the like described above and viscosity of the lubricant is further lowered in an environment severe in terms of lubrication, it becomes difficult to ensure an oil film thickness of a sliding surface of each engine portion. Consequently, lubrication of the sliding surface becomes insufficient, and seizure of the sliding portion such as a bearing is likely. In particular, as considerable combustion load is applied to a connecting rod bearing, seizure of the bearing is more likely.